Telegraphy



Patented Jan. 28, 1930 UNITED STATES HOWARD D. COLMAN, OF ROCKFORD, ILLINOIS TELEGRAPHY No Drawing. Application filed April 17, 1926, Serial No. 102,812. Renewed. November 16, 1928.

The invention relates to telegraphic communication, and its general aim is to lower the cost of such communication.

The cost of telegraphic communication depends to a large extent upon the length of time required in the transmission of the message matter, and the time required in turn depends largely upon the number of current impulses which must be transmitted to represent such message matter. The present practice is to transmit ordinary message mat ter by the use of code combinations constituting signals which represent the letters of the alphabet, these signals being used collectively or in groups to spell out the words letter by letter. Since the number of impulses which must thus be used to transmit a word depends directly upon the number of letters in the word, the number of impulses required in the case of the average word constitutes a fixed limitation upon the capacity of a telegraph system for handling message matter.

The object of the invention is to overcome such limitation upon the line capacity by the use of signals constituted independently of the letters comprising the words represented thereby, to the end that the num ber of impulses which are required to be transmitted to represent ordinary message matter may be substantially reduced.

In transmitting a message according to my invention, I employ jointly word and letter codes whereby such words of a given message as are commonly used in average daily intercourse are transmitted by means of signals individually representing such words and composed of code combinations of a relatively small number of units capable of being represented by either positive or negative, or current and no current impulses; and whereby the remaining words of the message are transmitted letter by letter by means of signals representing letters of the alphabet. The great majority of the words used in average daily intercourse may be transmitted by means of word signals, with a substantial saving in line time as compared with the methods now in use, and only words which. are normally need. with less frequency, proper names, and the like, need be transmitted letter by letter. I eliminate the necessity for using space signals between word signals by making all of the word signals of a particular kind or character. For example I employ in the present instance signals of uniform length, that is to say, composed of the same number of units, to represent words, While the signals representing letters are also composed of the same number of units but of a lesser number than the number of units composing the word signals. lVhen a change from word-code signals to letter-code signals is to be made, I employ a special code-change signal having the same number of units as the word-code signals, and likewise when a change is to be made from letter-code signals to word-code sig nals, I provide a special code-change signal having the same number of units as the letter-code signals. Thus each code, because of the difference in the number of units employed in their respective signals, includes a code-change signal.

Proceeding now to a more detailed consideration of my invention, the word-code signals are composed of combinations of an equal number of units having two or more interchangeable difierentiating characteristics. Thus they may be of the general type now commonly used in the Baudot code, wherein each unit has two differentiating characteristics and is represented by either a positive or negative impulse.

The number of units employed in each of the word-code signals is determined by the number of different code combinations to be provided, or, in other words, by the number of words comprising the limited vocabulary. In practice, the number of words comprising such vocabulary may be determined on the basis of the frequency with which words are used in daily intercourse. An investigation made for this purpose disclosed that in a file of ordinary incoming business correspondence the 32 most frequently recurring words were found to be used approximately 47% of the time; 1000 words approximately 91% of the time; and 2000 words approximately 96% of the time. u

Assuming, for the sake of illustration, that the arearranged vocabulary of words to be transmitted by means of word-code signals contains 2000 words, the desired number of different code combinations may be obtained by the use of 11 units, each capable of being represented by either a positive or negative current impulse. This is in accordance with the known mathematical formula 9 where N represents the number of units ineach code combination and p the number of different characteristics by which each unit may be represented. The use of 11 units gives, according to this formula, 2048 combinations available for assignment to the words of the word-code vocabulary.

The present embodiment of my invention contemplates preferably the employment, in the letter-code signals, only a sufficient number of units to provide for all of the letters or characters which it may be desired to transmit. Thus the letter signals may be composed of 5-unit code combinations or 32 in all. Because of the uniform length of the letter signals, a space signal is unnecessary to be employed between the individual letter signals, and it is only necessary to distinguish between two words transmitted by means of the letter-code and following in succession. However, inasmuch as the great majority of words are represented by word signals, the occurrence of two words in succession which must be represented by letter signals will be the exception rather than the rule.

In order that letter signals of a smaller number of units than the word signals may be employed, 1 provide a special or codechange signal and in the present instance I employ such a signal in each of the wordand letter-codes. Thus the word-code includes a special signal having the same number of units as the other signals therein indicating a change from the word-code to the letter-code, and likewise the letter-code has a special code signal therein to indicate a change from the letter-code to the wordcode.

It will be understood that the use o1 codechange signals is rendered unnecessary where the word and letter code signals are of the same length. Such system is fully set forth in my copending application Serial No. 102,813, filed April 17, 1926, and is within the contemplation of my invention as hereinafter claimed.

To illustrate the saving efiected by my in vention, it may be assumed that ll-unit wordecode signals are provided for each word i of a given vocabulary containing approximately 2000 words, and that a message containing 100 words is to be transmitted. Since on the basis of the above mentioned investigation 96 of these words would fall within the given vocabulary, the transmission of 11- unit word-code signals representing the 96 words would require 1056 impulses. The 4 remaining words, which may be reasonably assumed to have an average of 7 letters each and require the transmission of 5-unit lettercode signals, would require 140 impulses. A maximum of 15 impulses would be needed to indicate spaces between the 4- words (assuming that these words follow in succession) and two code-change signals, one of 11 units at the beginning of the transmission of letter signals, and one of 5 units at the end of the transmission of letter signals would be employed. Thus a totalof 122-7 impulses would be employed to transmit 100 words, 4 of which are transmitted by means of letter signals.

In transmitting a group of 100 words averaging 5 letters each by the use of the Baudotcode, it is necessary to send 25 impulses for the letters of each word, or 2500, and 5 impulses for each of the spaces between the words, or 500, making a total of 3000 impulses.

Thus it is evident that by means of my mately two and one-half times greater than in the case of the Baudot codal system.

in the foregoing illustration it has been assumed that only one word-code would be employed in addition to the letter code. it may, however, in some instances, be desired to provide two or more separate groups of words each represented by a different word code. For example, in addition to an 11- unit word code such as above described, a word code composed of 18-unit combinations may be provided, and it will be obvious that such a code may represent a much larger number of words. Thus according to the formula W, 18 units would give 262,144 different combinations each of which is available for assignment to a particular word.

With this arrangement, substantially all of the words of the language may be represented individually by word code signals and it is only necessary to provide special codechange signals indicating a change from one code to another. Thus each of the wordand letter codes would in this event have two.

to employ space signals between each of the word signals, or space signals between each of the letter signals no substantial saving would be elfected.

It will also be apparent that in so far as the transmission of word and letter signals in accordance with my invention is concerned,

existing apparatus may be employed except, of course, that the apparatus must be adapted to send signals containing the proper number of units as required for the difi'erent codes.

While any preferred method may be employed for coding and decoding the signals, it is contemplated that automatic mechanisms will be employed for this purpose, but inasmuch as these mechanisms form no part of this invention, it is deemed unnecessary to illustrate and describe them herein. It should be noted, however, that the use of such automatic coding and decoding mechanisms is greatly facilitated by the useof uniform length signals.

Another embodiment of the generic invention herein disclosed and claimed forms the subject matter of my co-pending application, Serial No. 102,813. filed April 17, 1926.

I claim as my invention:

1. In a telegraphic communication system in which signals each composed of a direct succession of units having two or more differentiating characteristics are transmitted electrically, the method of signalling which consists in transmitting word signals individually representing such words as fall within a given vocabulary, transmitting letter signals individually representing letters of the alphabet and spelling out letter by letter such words as fall outside the given vocabulary, while forming all of said signals so that as they occur in direct succession with no space signals between them they are capable of being distinguished from each other, and sending a space signal between the adjacent terminal letter signals of successive non-vocabulary words.

2. In a telegraphic communication system in which signals each composed of a direct succession of units having two or more differentiating characteristics are transmitted electrically, the method of signalling which consists in transmitting word signals each having the same number of units and inclividually representing such words as tall within a given vocabulary, transmitting letter signals individually representing letters of the alphabet to spell out letter by letter such words as fall outside the given vocabulary, and sending a space signal between the adjacent terminal letter signals of successive nonvocabulary words.

3. In a telegraphic communication system in which message matter is transmitted electrically by means of signals each composed of combinations of units occurring in direct succession, the method of signalling which consists in transmitting word signals each having a predetermined number of units and individually representing such words as fall within a given vocabulary, transmitting letter si nals each composed of the same number ot units but ditlerent from the number of units employed in the word signals, so as to spell out letter by letter such words as fall outside the given vocabulary, inserting a special signal between the adjacent terminal letter signals of successive words spelled out letter by letter, and inserting a special signal between word and letter signals to indicate a change from word signals to letter signals and vice versa.

4. In a telegraphic communication system in which message matter is transmitted electrically by means of signals each composed of combinations of units occurring in direct succession, the method of signalling which consists in transmitting word signals each having a predetermined number of units and individually representing such words as fall within a given vocabulary, transmitting letter signals each composed of the same number of units but dilterent from the number of units employed in the word signals, so as to spell out letter by letter such words as fall outside the given vocabulary, inserting a predetermined combination of units constituting a space signal between the adjacent terminal letter signals of successive words spelled out letter by letter, transmitting a special signal of the same number of units as the word signals to indicate a change from word to letter signals, and sending a special signal or" the same number of units as the letter signals to indicate a change from letter signals to word signals.

In a telegraphic communication system in which signals each composed of a direct succession of units having two or more difterentiating characteristics are transmitted electrically, the method of signalling which comprises transmitting, according to a prearranged word code, word signals each having the same number of units and individually representing such words as fall within a given vocabulary, transmitting, according to a prearranged letter code, letter signals individually representing letters of the alphabet to spell out letter by letter such words as fall outside the given vocabulary, sending a preconcerted signal combination to indicate a space between the adjacent terminal letter signals of successive non-vocabulary words, and sending a special signal combination to indicate a change from the letter code to the word code.

6. In a telegraphic communication system in which message matter is transmitted electrically by means of signals each composed of combinations of units occurring in direct succession, the method of signalling which comprises transmitting word signals each having a predetermined number of units and inclividually representing such words as tall within a given vocabulary, transmitting letter signals each composed of the same number of units but difierent from the number of units employed in the word signals, so as to spell out letter by letter such words as fall outside the given vocabulary, inserting a 'predeten mined combination of units constituting a space signal between the adjacent terminal letter signals of successive Words spelled out letter by letter, and transmitting'a special signal of the same number of units as the letter signals to indicate a change from letter signals to Word signals.

In testimony whereof, I have hereunto affixecl my signature.

HOWARD D. COLMAN. 

